For discussion and questions related to CMS Specific templates and stylesheets (CSS), and themes. or layout issues. This is not a place for generic "I don't know CSS issues"
The pagewrapper is styled in the stylesheet, but IE6 doesn't understand the min-max there, so the logic of the width for IE6 and below is done in the template.
It is not going to help you but I'd like to state that the page width is set by the browser display and is not a requirement of the content broadcaster. There are people with large screens, little screens, rotable screens. There are people how want to print your pages with landscape orientation, two on a sheet, etc. You should let people choose the width of theirs windows on their desktops. My 0.01¤.
Pierre M.